The present invention relates to a process for analyzing charged particles and more particularly a process for analyzing a sample with a resist which is sensitive to charged particles.
In general, in order to determine the masses of atoms or molecules found in a sample of gas, liquid or solid, a mass spectrometer and a mass spectrograph have been used. With a mass spectrometer, an analysis cannot be completed within a short time because of the unsteady nature of an ion beam. That is, the output current for a specific isotope from an electron multiplier of the mass spectrometer must be integrated for a predetermined time interval so that a correct mass may be determined. As a result, much time and labor are required for assaying a large number of ions found in a sample. Furthermore result attainable with a mass spectrometer is almost equal to result attainable by a mass spectrograph.
A mass spectrograph is advantageous in various respects over a mass spectrometer. First, all of atoms found in a very small quantity of a sample may be simultaneously analyzed with a higher degree of resolution, a more definite relation between mass and position in a mass spectrum and a high S/N ratio. Secondly, interference lines due to the presence of hydrocarbons and multiple charge ions may be clearly separated from peak lines. Thirdly, a wide mass spectrum may be obtained.
With a mass spectrograph, a specific isotope is in general exposed several times at different exposure levels in order to obtain a peak line of this isotope. However, there is not available a photographic emulsion capable of making equal records of all of the charged particles, and a photographic plate cannot be adjusted so as to be sensitive particularly to a selected charged particle.
In order to assay a mass spectrum obtained with a mass spectrograph, a microphotometer is used to measure blackness or the area of a peak line, but various errors result. When an extremely fine parallel light beam is impinged on a negative, some is specularly transmitted and some is scattered by a vast number of silver particles in an emulsion layer. Blackness measured in terms of all the transmitted light is referred to as diffused blackness while blackness measured in terms of only the light passing directly through the negative is referred to as specular blackness. However specular blackness is not absolutely correct because the microphotometer also picks up light reflected from the negative. Diffused blackness is also inaccurate because the microphotometer picks up light transmitted laterally of the negative. That is, the blackness measured varies depending upon an illumination system and an optical measurement system of the microphotometer so that the analytical results in terms of blackness also vary.